Common Share Capitalization (Narrative) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Jun. 13, 2018
Common Stock Capitalization [Line Items]
Dividends declared (in usd per share)	$ 0.41	$ 0.45	$ 1.23	$ 1.35
Payments of Dividends	$ (12,700)	$ (14,800)	$ (38,152)	$ (44,336)
Common Shares Issued And Outstanding Upon Conversion of All Convertible Securities	30,871,043	32,680,917	30,871,043	32,680,917
Stock Repurchase Program, Number of Shares Authorized to be Repurchased					1,550,000
Shares repurchased	0	123,321	1,186,058	305,327
Stock Repurchased and Retired During Period, Value			$ 17,593	$ 4,791
Stock Repurchases, Average Price Per Share			$ 14.83